Allergic diseases such as atopic dermatitis are considered to be multifactorial diseases. Multifactorial diseases are caused by the interaction of many different genes, the expression of each of which is independently influenced by multiple environmental factors. Thus, determining the specific genes that cause a specific allergic disease is extremely difficult.
Allergic diseases are generally presumed to be associated with the expression of genes having mutations or defects, and/or with the overexpression or reduced expression of specific genes. To determine the role of gene expression in a disease, it is necessary to understand how genes are involved in the onset of that disease, and how gene expression is altered by external stimulants such as drugs.
Recent developments in gene expression analysis techniques have enabled analysis and comparison of gene expression in multiple clinical samples. As an example of such methods, the differential display (DD) method is useful. Liang and Pardee originally developed this method in 1992 (Science, 1992, 257: 967–971). By using this method, several dozen or more samples can be screened at one time, thereby enabling the detection of genes whose expression in one sample differs from other samples. Information essential to determining the causative gene(s) of a disease is expected to be obtained by examining genes with mutations, or genes whose expression changes depending on time and the environment, including genes whose expression is influenced by environmental factors.
Recently, patient interviews and patient medical and family history have become important factors in the diagnosis of allergic disease. More objective methods of diagnosing allergies include testing patient blood samples and observing patient immune response to allergen(s). Examples of the former method include allergen-specific IgE measurement, the leukocyte histamine release test and the lymphocyte blast transformation test. The presence of allergen-specific IgE is evidence of an allergic reaction against an allergen. However, allergen-specific IgE is not always detected in every patient. Furthermore, in principle, IgE assaying requires tests to be performed on all of the allergens necessary for diagnosis. The leukocyte histamine release test and the lymphocyte blast transformation test are methods for observing immune system reaction towards a specific allergen in vitro. Operation of these methods is complex.
Another known method useful in allergy diagnosis is based on the immune response observed when a patient contacts an allergen (i.e., the latter method). Such tests include the prick test, scratch test, patch test, intradermal reaction and induction test. These tests allow direct diagnosis of a patient's allergic reaction, but are highly invasive as patients are actually exposed to allergens.
Methods of confirming the involvement of an allergic reaction, regardless of allergen type, are also being trialed. For example, a high serum IgE titer indicates an allergic reaction in a patient. The serum IgE titer corresponds to the total amount of allergen-specific IgE. Determining the total amount of IgE is simple, regardless of the type of allergen; however, IgE titer may be reduced in some patients, for example, in those with non-atopic bronchitis.
The number of eosinophils and the level of eosinophil cationic protein (ECP) are diagnostic items for delayed-type reactions following Type I allergy-and allergic inflammatory reactions. The number of eosinophils is considered to reflect the progress of allergic symptoms. ECP, a protein contained in eosinophil granules, is also strongly activated in patients having an asthma attack. Although allergic symptoms can indeed be identified using these diagnostic items, the extent to which they can actually be used as diagnostic indices is limited.
Therefore, diagnostic indices useful in understanding pathological conditions in patients with allergic diseases, and in determining treatment regimens for such diseases, regardless of the type of allergen, have been greatly sought after. Allergic disease markers that are less risky for patients and capable of readily providing information required for diagnosis would be of great use. If genes associated with allergic disease can be identified, the expression of such genes can be used as an index to test for allergic diseases. Furthermore, if the cellular function of proteins encoded by these genes can be elucidated, observations regarding these functions can be used as a base to promote the development of therapeutic methods and pharmaceutical agents for treating allergic diseases.